1 ASoC Codec Class Driver
2 =======================
4 The codec class driver is generic and hardware independent code that configures
5 the codec, FM, MODEM, BT or external DSP to provide audio capture and playback.
6 It should contain no code that is specific to the target platform or machine.
7 All platform and machine specific code should be added to the platform and
8 machine drivers respectively.
10 Each codec class driver *must* provide the following features:-
12 1) Codec DAI and PCM configuration
13 2) Codec control IO - using RegMap API
14 3) Mixers and audio controls
15 4) Codec audio operations
17 6) DAPM event handler.
19 Optionally, codec drivers can also provide:-
21 7) DAC Digital mute control.
23 Its probably best to use this guide in conjunction with the existing codec
24 driver code in sound/soc/codecs/
26 ASoC Codec driver breakdown
27 ===========================
29 1 - Codec DAI and PCM configuration
30 -----------------------------------
31 Each codec driver must have a struct snd_soc_dai_driver to define its DAI and
32 PCM capabilities and operations. This struct is exported so that it can be
33 registered with the core by your machine driver.
37 static struct snd_soc_dai_ops wm8731_dai_ops = {
38 .prepare = wm8731_pcm_prepare,
39 .hw_params = wm8731_hw_params,
40 .shutdown = wm8731_shutdown,
41 .digital_mute = wm8731_mute,
42 .set_sysclk = wm8731_set_dai_sysclk,
43 .set_fmt = wm8731_set_dai_fmt,
46 struct snd_soc_dai_driver wm8731_dai = {
47 .name = "wm8731-hifi",
49 .stream_name = "Playback",
52 .rates = WM8731_RATES,
53 .formats = WM8731_FORMATS,},
55 .stream_name = "Capture",
58 .rates = WM8731_RATES,
59 .formats = WM8731_FORMATS,},
60 .ops = &wm8731_dai_ops,
67 The codec can usually be controlled via an I2C or SPI style interface
68 (AC97 combines control with data in the DAI). The codec driver should use the
69 Regmap API for all codec IO. Please see include/linux/regmap.h and existing
70 codec drivers for example regmap usage.
73 3 - Mixers and audio controls
74 -----------------------------
75 All the codec mixers and audio controls can be defined using the convenience
76 macros defined in soc.h.
78 #define SOC_SINGLE(xname, reg, shift, mask, invert)
80 Defines a single control as follows:-
82 xname = Control name e.g. "Playback Volume"
84 shift = control bit(s) offset in register
85 mask = control bit size(s) e.g. mask of 7 = 3 bits
86 invert = the control is inverted
88 Other macros include:-
90 #define SOC_DOUBLE(xname, reg, shift_left, shift_right, mask, invert)
94 #define SOC_DOUBLE_R(xname, reg_left, reg_right, shift, mask, invert)
96 A stereo control spanning 2 registers
98 #define SOC_ENUM_SINGLE(xreg, xshift, xmask, xtexts)
100 Defines an single enumerated control as follows:-
103 xshift = control bit(s) offset in register
104 xmask = control bit(s) size
105 xtexts = pointer to array of strings that describe each setting
107 #define SOC_ENUM_DOUBLE(xreg, xshift_l, xshift_r, xmask, xtexts)
109 Defines a stereo enumerated control
112 4 - Codec Audio Operations
113 --------------------------
114 The codec driver also supports the following ALSA PCM operations:-
118 int (*startup)(struct snd_pcm_substream *);
119 void (*shutdown)(struct snd_pcm_substream *);
120 int (*hw_params)(struct snd_pcm_substream *, struct snd_pcm_hw_params *);
121 int (*hw_free)(struct snd_pcm_substream *);
122 int (*prepare)(struct snd_pcm_substream *);
125 Please refer to the ALSA driver PCM documentation for details.
126 http://www.alsa-project.org/~iwai/writing-an-alsa-driver/
129 5 - DAPM description.
130 ---------------------
131 The Dynamic Audio Power Management description describes the codec power
132 components and their relationships and registers to the ASoC core.
133 Please read dapm.txt for details of building the description.
135 Please also see the examples in other codec drivers.
138 6 - DAPM event handler
139 ----------------------
140 This function is a callback that handles codec domain PM calls and system
141 domain PM calls (e.g. suspend and resume). It is used to put the codec
142 to sleep when not in use.
146 SNDRV_CTL_POWER_D0: /* full On */
147 /* vref/mid, clk and osc on, active */
149 SNDRV_CTL_POWER_D1: /* partial On */
150 SNDRV_CTL_POWER_D2: /* partial On */
152 SNDRV_CTL_POWER_D3hot: /* Off, with power */
153 /* everything off except vref/vmid, inactive */
155 SNDRV_CTL_POWER_D3cold: /* Everything Off, without power */
158 7 - Codec DAC digital mute control
159 ----------------------------------
160 Most codecs have a digital mute before the DACs that can be used to
161 minimise any system noise. The mute stops any digital data from
164 A callback can be created that is called by the core for each codec DAI
165 when the mute is applied or freed.
169 static int wm8974_mute(struct snd_soc_dai *dai, int mute)
171 struct snd_soc_codec *codec = dai->codec;
172 u16 mute_reg = snd_soc_read(codec, WM8974_DAC) & 0xffbf;
175 snd_soc_write(codec, WM8974_DAC, mute_reg | 0x40);
177 snd_soc_write(codec, WM8974_DAC, mute_reg);